JPH0982651A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a single crystal silicon film, which has little crystal defect or the like, on a silicon substrate using a solid phase growth method. SOLUTION: When a single crystal silicon substrate 1 is housed in a film- forming chamber and film-forming gas is introduced in the chamber to form an amorphous silicon film 3 on the substrate 1, a substrate temperature is set lower than that at the time of the formation of the film 3 before the introduction of the film-forming gas to introduce Si2 H6 gas in the chamber as reducing gas. After that, the film 3 is changed into a single crystal silicon film 3a by a solid phase growth using the substrate 1, which is subjected to heat treatment, as a seed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for suppressing oxidation of a semiconductor surface.

[0002]

2. Description of the Related Art In recent years, a large-scale integrated circuit (IC) formed by integrating a large number of transistors, resistors and the like into an important part of a computer or a communication device so as to achieve an electric circuit has been integrated on one chip. LSI) is frequently used. For this reason, the performance of the entire device is greatly related to the performance of the LSI alone.

[0003] The performance of an LSI alone can be improved by increasing the degree of integration, that is, by miniaturizing elements. Conventionally, miniaturization has been attempted by various techniques. As miniaturization technology, for example, partial SOI and reduction of contact resistance are required.

As one of the methods for partial SOI, a method of partially forming SOI on a substrate by using a solid phase growth method has been attempted. Specifically, first, an insulating film (SOI insulating film) is formed on part of a single crystal silicon substrate. Next, an amorphous silicon film is formed on the entire surface at a low temperature of about 400 to 600 ° C., and then 500 to 600 is formed on the amorphous silicon film.
The amorphous silicon film is single-crystallized in a solid state by heat treatment at a low temperature of about ℃, and the single-crystal silicon film (SO
I silicon film). Finally, the single crystal silicon film on the silicon substrate is removed to complete the SOI structure on a part of the silicon substrate.

According to this method, there is an advantage that the SOI can be formed at a low temperature which does not cause redistribution of impurities in the substrate. That is, it has an advantage that it can be incorporated into an actual LSI manufacturing process.

However, this method has the following problems and is difficult to use in practice. The main reason for this is that the single crystallization is hindered by impurities such as oxides existing at the interface between the amorphous silicon film and the seed silicon substrate during the single crystallization. As a result,
A large number of crystal defects occur in the SOI silicon film, or the SOI silicon film has a polycrystalline structure in some cases.

Partial SOI created by such a conventional technique
When an enhancement type n-type MOSFET is created in
The movement is 200 to 400 cm ² / Vsec, which is 1 / th that of a normal single-crystal silicon substrate.
The value is as low as 2 to 1/3. There is also a problem that the leak current is large as compared with the case where it is formed on a single crystal silicon substrate.

On the other hand, in order to reduce the contact resistance, it is necessary to prevent the formation of an oxide film such as a natural oxide film or a nitride film at the interface between two conductive layers (eg, wiring). This can be achieved, for example, by using an exhaust facility that can achieve a high vacuum (up to 1 × 10 ⁻⁸ Pa), but there is a problem in that it is costly.

[0009]

As described above, a method of partially forming an SOI on a silicon substrate by using the conventional solid-phase growth method has been attempted. However, a method of forming a silicon substrate and an amorphous silicon film is used. There has been a problem that the single crystal of the amorphous silicon film is hindered by impurities such as oxides at the interface.

The present invention has been made in consideration of the above circumstances, and an object thereof is a method of manufacturing a semiconductor device capable of preventing oxidation at an interface between two films such as a semiconductor film / semiconductor film at low cost. To provide.

[0011]

[Means for Solving the Problems]

[Summary] In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention (claim 1) includes a step of housing a semiconductor substrate in a container, and the container until the inside reaches a film formation temperature. Introducing a gas containing a reducing gas into the interior,
After introducing the reducing gas into the container, introducing a film forming gas into the container to form a film on the semiconductor substrate.

Here, the film is a conductive film, a semiconductor film or an insulating film, and the base of the film is also a conductive film, a semiconductor film (including the semiconductor substrate itself) or an insulating film.

Another method for manufacturing a semiconductor device according to the present invention (claim 2) is the same as the method for manufacturing a semiconductor device (claim 1), wherein the semiconductor substrate is a silicon substrate, and the film forming gas is disilane gas. One gas selected from trisilane gas and tetracine gas or a mixed gas of two or more gases is featured.

[Function] The inventors of the present invention have investigated the reoxidation of the surface of the silicon substrate from which the natural oxide film has been removed. As a result, the oxidizing substances such as water and oxygen remaining in the semiconductor manufacturing apparatus have large reoxidation. It became clear that it was the cause.

That is, it has been considered that the condition inside the semiconductor manufacturing apparatus is usually well controlled, and the remaining amount of oxidizing substances such as water and oxygen inside the apparatus is small, and these cannot cause reoxidation. , In fact, was found to be a major cause of reoxidation.

In order to sufficiently reduce the residual amount of oxidizing substances such as water and oxygen in the apparatus, high vacuum (up to 1 × 10 ^-8 Pa) is used.
This is possible by using an exhaust system that can achieve the above, but it will be costly.

Therefore, according to the present invention, a gas containing a reducing gas is introduced into the container until the film forming temperature is reached in the container, and then the film forming gas is introduced into the container to remain in the container. The oxidation by the oxidative substance and the oxidization caused by the oxidative substance outside the container being introduced into the container are prevented at low cost.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a MOS according to an embodiment of the present invention.
6A to 6C are process cross-sectional views illustrating a method for forming a transistor.

First, as shown in FIG. 1A, a shallow groove is formed on the surface of a single crystal silicon substrate 1. Then, the groove is filled with the element isolation insulating film 2 to perform element isolation.

Next, as shown in FIG. 1B, the amorphous silicon film 3 is formed on the element forming region and on the element isolation insulating film 2 in the portion in contact with the element forming region by the CVD method.
To form

As the CVD apparatus, for example, one having the structure shown in FIG. 2 is used.

This is a 6-inch vertical LPCVD apparatus with dry pump specifications. In the figure, 21 is a film forming chamber C
A VD furnace is shown, and this CVD furnace 21 can accommodate a plurality of substrates (wafers). CVD furnace 2
A heater 23 is provided around 1, and a dry pump 36 is provided below the CVD furnace 21. The film forming gas (process gas) is the pipe 24, the mass flow controller 2
5, it is introduced into the CVD furnace 21 through the filter 26 and the valve 27. Similarly, the inert gas is introduced into the CVD furnace 21 through the pipe 28, the mass flow controller 29, the filter 30, and the valve 31. Similarly, the reducing gas is used for the pipe 32, the mass flow controller 33, and the filter 3.
4, it is introduced into the CVD furnace 21 through the valve 35.

In this embodiment, the silicon substrate 1 is subjected to CVD.
The amorphous silicon film 3 is housed in the film forming chamber 21 of the apparatus.
However, before introducing the film-forming gas for forming the amorphous silicon film 3 into the film-forming chamber 21, the reducing property is reduced in the film-forming chamber 21 until the temperature in the film-forming chamber 21 reaches the film-forming temperature. Disilane gas is introduced as a gas to reduce oxidizing substances such as water and oxygen in the film forming chamber 21.

This makes it possible to prevent the generation of oxides at the interface between the semiconductor substrate 1 and the amorphous silicon film 3. Note that trisilane gas or tetracine gas may be used instead of disilane gas. Furthermore, a mixed gas of two or more selected from disilane gas, trisilane gas and tetracine gas may be used. Alternatively, it may be used as a mixture with another gas such as an inert gas.

Next, as shown in FIG. 1C, a gate oxide film 4 is formed on the surface of the amorphous silicon film 3. The gate oxide film 4 is preferably formed by, for example, thermal oxidization after crystallizing the amorphous silicon film 3 by heat treatment.

Next, as shown in FIG. 3C, after forming a polycrystalline silicon film to be the gate electrode 5 on the entire surface, the polycrystalline silicon film is patterned to form the gate electrode 5. At this time, the gate oxide film 4 is also patterned at the same time. The above-mentioned polycrystalline silicon film is formed, for example, by CVD using silane gas as a source gas at a substrate temperature of 620 ° C.
It is formed by the method.

Next, as shown in FIG. 3C, an insulating film such as an oxide film or a nitride film to be the gate sidewall insulating film 6 is formed on the entire surface, and then this insulating film is anisotropically formed by reactive ion etching. Etching is performed to selectively leave the side wall of the gate portion (gate electrode 5, gate oxide film 4).

Next, as shown in FIG. 1D, impurities are ion-implanted into the amorphous silicon film 3 by using the gate sidewall insulating film 6 and the gate portion (gate electrode 5, gate oxide film 4) as a mask, For example, the source region 7 and the drain region 8 are formed by activating the impurities by annealing at 850 ° C. In the case of p-type MOSFET, for example, B (boron) is used as the impurity, and n-type MOSFET is used.
In the case of T, As (arsenic) and P (phosphorus) are used.

Next, as shown in FIG. 3E, the amorphous silicon film 3 is formed into a single crystal by solid phase growth using the single crystal silicon substrate 1 as a seed by heat treatment at 600 ° C. for 2 hours in a nitrogen atmosphere. Change to the silicon film 3a. Further, this heat treatment may be performed immediately after the same figure (b), that is, immediately after forming the amorphous silicon film 3, to perform solid phase growth.

At this time, in the step of FIG. 1B, the amorphous silicon film 3 is formed so that no oxide is generated at the interface between the semiconductor substrate 1 and the amorphous silicon film 3, so that the amorphous silicon film 3 is formed. Does not hinder the single crystallization of. Therefore, unlike the conventional case, a large number of crystal defects do not occur in the single crystal silicon film 3a, and a part or all of the single crystal silicon film 3a does not become polycrystalline.

The heat treatment temperature may be higher than 600 ° C. as long as it does not interfere with other steps. Also, 60
Even if the temperature is lower than 0 ° C., it can be changed to the single crystal silicon film 3a by prolonging the heat treatment time.

Finally, as shown in FIG. 3E, a conductive film such as an aluminum film to be the source electrode 9 and the drain electrode 10 is formed by the CVD method, and then the conductive film is patterned to form the source electrode 9, The drain electrode 10 is formed to complete the MOSFET.

At this time, as in the case of the amorphous silicon film 3, a reducing gas such as disilane is introduced before introducing the raw material gas for the conductive film into the film forming chamber to remove the oxidizing substance in the film forming chamber. Give back. As a result, it is possible to prevent the generation of oxide at the interface between the conductive film and the single crystal silicon film 3a in the source region 7 and the drain region 8. Therefore,
It is possible to prevent the source contact resistance and the drain contact resistance from rising.

Further, according to the present embodiment, since the element isolation insulating film 2 exists under the source region 7 and the drain region 8, when the lower parts of the source region 7 and the drain region 8 are all semiconductor films. Compared with this, the amount of charges accumulated under the source region 7 and the drain region 8 is small, which is advantageous for speeding up.

According to the forming method of the present embodiment, 0.4 μm
A CMOS ring oscillator was created according to the rules, and its delay time was measured to be 40 psec / stas.
It was ge. On the other hand, when the delay time of the CMOS ring oscillator produced according to the conventional forming method was measured, it was 50 psec / stage.

From these results, it was found that by using the forming method of this embodiment, the delay time can be shortened by 20% as compared with the conventional case. Further, when the source electrode 9 and the drain electrode 10 are in contact with the source region 7 and the drain region 8 respectively through the contact holes formed in the interlayer insulating film, the delay time is 25 p.
It could be shortened to sec / stage. However, when this structure is formed using the conventional method, unlike the present embodiment, the crystallinity is poor and the leak current increases, and the LS
It could not be used for the I circuit.

Although the present embodiment has been described for the case where the trench isolation (STI method) is used as the element isolation method, the present invention can be applied to the case where the LOCOS method is used as the element isolation method.

Next, experiments and the like which are the basis of creation of the present invention will be described.

In order to clarify the cause of reoxidation of the surface of the silicon substrate from which the native oxide film has been removed, the present inventors formed an experimental system as shown in FIG. The gas components in the CVD device were analyzed.

The CVD apparatus is a 6-inch vertical LPCVD apparatus with a dry pump specification, and the dry pump 36 has a displacement of 7,000 liters. As the gas analyzer 39, a Q-Mass gas analyzer was used. Q-Mas
The sensitivity of s was calibrated by Ar gas (0.1 Torr) introduced into the apparatus through the Ar line.

Further, the dew point meters 37 and 38 are of a type in which the water content is obtained from the resistance change of the surface of the porous Al ₂ O ₃ due to the H ₂ O adsorption. This type of dew point meter can measure the amount of water even under a reduced pressure lower than 1 atm.

First, when the valve 41 is closed, the valve 40 is opened, and the inside of the CVD furnace 21 is evacuated by a dry pump so that the ultimate vacuum is about 5 × 10 ⁻³ Torr (0.6 Pa), it is shown in FIG. as the partial pressure of residual gas, H ₂ O is 5 × 10 ^-3 Torr, N ₂ is ₂ × 10 ^-3 Torr, O 2
Was 2 × 10 ⁻⁴ Torr (× 133 Pa). That is, the residual gas in the CVD apparatus was mainly H ₂ O.

As shown in FIG. 4, N ₂ is also detected.
This is because the atmosphere side of the dry pump 36 is purged with N ₂ to dilute the exhaust of the source gas such as Si ₂ H ₆ , and this N ₂ flows backward.

Next, when Ar gas is introduced at 230 SCCM and the total pressure is set to 0.1 Torr, the partial pressure of Ar is 8 × 10 ^-2.
The partial pressure of Torr and H ₂ O is 7 × 10 ⁻³ Torr, the partial pressure of N ₂ is 4 × 10 ⁻⁴ Torr, and the partial pressure of O ₂ is 3 × 10 ⁻⁴ T.
It became orr (× 133 Pa).

As shown in FIG. 5, the backflow of N ₂ from the atmospheric side to the vacuum side of the pump is prevented by the flow of Ar, and N ₂ in the apparatus is reduced by one digit. However, even if Ar is introduced, H
₂ O and O ₂ do not decrease immediately.

In order to check the remaining place of H ₂ O, the valve 4
Changes in the partial pressure of the residual gas were measured while opening and closing 0 and 41. The results are shown in FIG.

During the period a, a full scale calibration of the gas analyzer 39 was performed using Ar gas.

The period b is a period in which the valve 40 between the CVD apparatus and the dry pump 36 is closed in order to investigate the characteristics of only the dry pump 36. When only the dry pump 36 reached the ultimate vacuum, H ₂ O was not exhausted any more.

During the period c, the valve 40 is opened and the dry pump 3
6 was connected to the CVD apparatus body, the exhaust did not proceed beyond the reachability of the dry pump 36.

The period d is a period in which Ar is introduced. N ₂
Is reduced because the backflow from the dry pump 36 is suppressed,
H ₂ O increases rather slightly. This is due to the measuring method. That is, it is considered that the gas analyzer 39 and the CVD furnace 21 were connected via an orifice, and the flow of H ₂ O was amplified by the viscosity of Ar flowing through this orifice.

Period e is when Ar is switched to N ₂ . Ar decreases but 10 to replace N ₂
It turned out to take more than a minute. However, as in the case of introducing Ar, the introduction of N ₂ did not change the partial pressure of H ₂ O.

From the above results, it was found that H ₂ O was adsorbed on the entire apparatus, could not be exhausted beyond the capacity of the pump, and was difficult to be flushed with the introduced gas (Ar, N ₂ ). It was

Next, the change of H ₂ O adsorbed in the CVD apparatus due to heating was examined. FIG. 7 shows the result.

The temperature of the CVD furnace (substrate temperature) is set to room temperature (R.
T. ) To 600 ° C., the residual gas analysis was performed. As shown in FIG. 7, no change in H ₂ O partial pressure was observed. It is considered that H ₂ O was not desorbed from the furnace wall little, or that it was re-adsorbed at a low temperature place.

Further, the H ₂ partial pressure increases as the temperature rises. This is because the furnace in which the cleaning is not performed is used.
Probably because ₂ was released. H ₂ decreases with time.

Also, a trace amount of C ₆ H ₆ (benzene) was detected. It is considered that this is due to decomposition products such as oil and O-ring rubber.

Here, since it was doubtful that the H ₂ O partial pressure did not decrease when Ar was introduced, the water content in Ar gas was measured. When the dew point of Ar supplied from the Ar line is measured with the dew point meter B38 in FIG.
It was 79 ° C. (5 × 10 ⁻⁴ Torr). It is about 700 ppb in terms of water content.

When Ar gas containing about 700 ppb of H ₂ O was introduced into the furnace at 0.1 Torr to replace the atmosphere, the H ₂ O partial pressure was 0.1 × 7 × 10 ⁻⁷ To by simple proportional calculation.
It should be possible to reduce to rr.

Actually, Ar was introduced into the CVD furnace 21,
The dew point under reduced pressure was measured using a dew point meter A37 installed in the nozzle portion directly connected to the CVD furnace 21. As a result, as shown in the table below, Ar: 230SCCM,
In all cases of 0.1 Torr, 4000 SCCM, 1 Torr, and Ar stop 5 × 10 ⁻³ Torr, the dew point was −79 ° C. (H ₂ O partial pressure 5 × 10 ⁻⁴ Torr).

[0061]

[Table 1] After all, H ₂ O adsorbed and desorbed from all parts of the equipment such as the piping wall of the decompression section after the mass flow control 29.
It was found that the partial pressure was decided by and the Ar substitution was not possible. (It is considered that the value decreases if the purging is performed for a long time, but it did not change in the measurement for 30 minutes.) Therefore, the main factor of H ₂ O in the atmosphere in the CVD furnace 21 is not the water content in Ar, It was confirmed that it was adsorbed H ₂ O at room temperature such as the piping of the apparatus.

Thus, the reproducibility of H ₂ O remaining in the apparatus was examined. The partial pressure of residual H ₂ O in the device measured by using the gas analyzer is shown in FIG. Measurements were performed 4 times over 8 months, but no change was observed.

By the way, the experiment of Zwan et al. Using isotopes (MLW van derZwan, JAB)
ardwell, G.M. I. Sproule, and
M. J. Graham: Appl. Phys. Let
t. , Vol. 64, P.P. 446, 1994), the polarized complex of H ₂ O and O ₂ (H ₂ O / O ₂ complex) advances the oxidation of the silicon surface, and oxygen in H ₂ O is taken into the oxide film. .

From this fact, H remaining in the CVD apparatus
_{It is considered that 2} O re-oxidizes the surface of the silicon substrate from which the native oxide film has been removed with an HF solution or the like.

Therefore, H ₂ remaining in the CVD apparatus
In order to remove O and prevent the surface of the silicon substrate (silicon wafer) 22 from being oxidized, as shown in FIG. 2, a reducing gas introduction facility (reducing gas introduction pipe 3
2, the mass flow controller 33, the filter 34, the valve 35) may be additionally installed so that a reducing gas (for example, Si ₂ H gas) can be introduced.

Next, the action of introducing a reducing gas will be described.
The solid phase growth technique of silicon will be described below as an example.

Such a solid phase growth technique is roughly divided into three steps of pretreatment, formation of an amorphous silicon film, and crystallization heat treatment. The pretreatment is a step of removing the natural oxide film on the surface of the silicon substrate, and is performed using a hydrofluoric acid solution or the like. The amorphous silicon film is formed by
This is a step performed using a CVD apparatus, and is a step to which the present invention is applied. The crystallization heat treatment is a step of crystallizing the amorphous silicon film.

When the amorphous silicon film is formed, if the surface of the silicon substrate from which the natural oxide film has been removed by the pretreatment is reoxidized, the epitaxial growth of the amorphous silicon film is hindered.

FIG. 9 shows the results of examining the effect of suppressing oxidation on the surface of a silicon substrate when the present invention is applied to a CVD apparatus for forming an amorphous silicon film. That is, the atmosphere in the CVD furnace is set to vacuum, Ar, SiH ₄ , Si
₂ H ₆ was used to determine the atmosphere dependence of the amount of oxidation. As shown in FIG. 9, the amounts of oxidation are vacuum, Ar, SiH ₄ , and Si ₂ H.
It decreased in the order of ₆ atmospheres.

It can be seen from FIG. 9 that the effect of suppressing oxidation in the Si ₂ H ₆ atmosphere is particularly high. Also, even in a SiH ₄ atmosphere, S
It can be seen that the effect of suppressing oxidation is obtained, though not so much as in the i ₂ H ₆ atmosphere. Ar is 4000 sccm, Si ₂
H ₆ was set to 20 to 100 sccm.

In the case of Si ₂ H ₆ , for example, the amount of oxidation is determined according to the following process flow.

Deposition of amorphous silicon film (thickness 1
Approx. 00 nm) 480 ° C., 30 minutes, Si ₂ H ₆ = 100 SCCM, 0.3 Torr ・ Holding device atmosphere = vacuum exhaust, Ar (or Si
₂ H ₆ / Ar) ・ Amorphous silicon film deposition (thickness: about 100 nm) 480 ° C., 30 minutes, Si ₂ H ₆ = 100 SCCM, 0.3 Torr ・ Hold again Device atmosphere = vacuum exhaust, Ar (or Si ₂ H ₆ / Ar) (holding conditions (time, atmosphere) are changed and deposition / holding is repeated several times.)-Amorphous silicon film deposition (about 100 nm thick) 480 ° C., 30 minutes, Si ₂ H ₆ = 100 SCCM, 0.3 Torr SIMS Analysis FIG. 10 shows a typical example in which an amorphous silicon film is sequentially deposited by the above procedure.

The amount of oxidation in each atmosphere a to g was obtained from the amount of oxygen trapped in each interface S1 to S7. That is, regarding the oxygen peaks obtained by SIMS analysis, it was considered that all oxygen was present at the interface, and the peak area was defined as the interfacial oxygen amount. The analysis result in the depth direction by SIMS analysis is due to the knock-on effect due to sputtering during analysis.
It is known to have a certain width. Therefore,
By using the area, the oxygen amount can be obtained with high accuracy. When a multilayer structure is formed as shown in FIG. 10A, from the spectrum of FIG. 10B, if the film thickness of the amorphous silicon film between the interfaces is 100 nm,
It can be seen that each peak can be sufficiently separated and measured.

The action of this reducing gas, that is, the effect of reducing oxidation can be explained by the thermodynamic equilibrium calculation regarding the oxygen partial pressure.

FIG. 11 shows the amount of oxidation at 480 ° C./10 minutes when Ar was introduced and the pressure inside the apparatus was changed.

The amount of this oxidation is the amount of oxygen at the interface of the amorphous silicon film which is less than two monoatomic layers after being kept in Ar atmospheres having different flow rates for 10 minutes, respectively, by SIMS.
It was obtained by analysis. As shown in FIG. 11, when the pressure inside the apparatus increases to some extent, it becomes difficult for the oxidation to proceed.

As described above, in the case of oxidizing an amorphous silicon film having less than one atomic layer, the diffusion rate is not controlled, and H
_It can be assumed that when ₂ O molecules collide with the surface of the amorphous silicon film, they react with a certain probability.

The total number φ ₀ of molecules that collide with the unit area of the wall per unit time is calculated by the following equation.

[0079] _{φ 0 = n · v / 4} = P / (2πmkT) 1/2 ... (1) v = (8kT / πm) 1/2 ... (2) Here, φ ₀ is a molecular bundle, n is the unit Number of molecules per volume, v is the average speed of the molecule, P is the pressure, m is the mass of the molecule,
T is an absolute temperature and k is a Boltzmann constant.

In the CGS system, k = 1.38 × 10 ^-16 e
rg · K ⁻¹ , 1 Torr = 133.3 Pa = 1333 g
・ It becomes cm ^-1・ s ^-2 .

For example, when H ₂ O is 5 × 10 ⁻³ Torr, m = 18/6 × 10 ²³ g, so at 480 ° C., v = 94000 cm / s, φ ₀ = 1.5 × 10 ¹⁸
It becomes the number / s.

This is three orders of magnitude higher than the surface density of the amorphous silicon film of 1.3 × 10 ¹⁵ atoms / cm ² , and most of the H ₂ O molecules that collide with the amorphous silicon film oxidize the amorphous silicon film. It means to reflect without.

The reaction rate (the number of reaction molecules / the number of collision molecules) is estimated from the oxidation rate, and it is about 5 × 10 ⁻⁷ . Similarly, Ar
Is 1.2 Torr / 480 ° C, v = 63000c
m / s, φ ₀ = 2.4 × 10 ²⁰ pieces / s.

Therefore, H ₂ O and Ar collide with the surface of the silicon substrate in a large excess compared with the oxidation reaction rate,
The surface of the silicon substrate is occupied by the competition between H ₂ O and Ar. It can be explained that as the pressure of Ar increases, the probability that the surface of the silicon substrate is occupied by Ar increases, and the probability that H ₂ O directly collides with the silicon substrate decreases, so that the progress of oxidation slows.

FIG. 12 shows the JANAF Thermoch.
electronic Tables, NSRDS-NBS. ,
1971-1985. The equilibrium oxygen partial pressure calculated using is shown.

As shown in FIG. 12, H ₂ or SiH
_{Even with 4} gases, the oxygen partial pressure cannot be lower than the equilibrium oxygen partial pressure of the Si / SiO ₂ redox reaction.

On the other hand, Si ₂ H ₆ gas contains Si /
The oxygen partial pressure can be reduced below the equilibrium partial pressure of the SiO ₂ redox reaction.

Similarly, a higher-order silane gas such as trisilane or tetrasilane having a large reducing action can reduce the equilibrium oxygen partial pressure to be equal to or lower than the Si / SiO ₂ equilibrium oxygen partial pressure.

FIG. 13 shows SiO _{2 produced} by Si ₂ H ₆ gas.
The result of having measured the reduction amount of is shown. In the figure, a is Ar / 0.
When kept at 1 Torr for 1 hour, b is Ar / 0.1T
After holding at orr for 1 hour, Si ₂ H ₆ = 100s
The figure shows the case of exposure to ccm / Ar = 4000 sccm (1.2 Torr) for 1 hour. The amount of oxygen in the case of condition b is not reduced as compared with the case of condition a. Therefore,
No reduction of SiO ₂ by Si ₂ H ₆ has occurred.

As a result of examining only the amount of Si ₂ H ₆ deposited at the time of heat recovery by a sectional TEM without depositing the amorphous silicon film, the thickness of the silicon film formed on the substrate was 4.3 nm. Immediately after formation, it was already a single crystal.

480 ° C., Si ₂ H ₆ pressure = 0.3 Tor
The film formation rate at r is 4 nm / min. Since the total pressure during heat recovery is 1.2 Torr and the Si ₂ H ₆ partial pressure is 0.03 Torr, assuming that the film formation rate is proportional to the partial pressure, it is 0.4 nm / min.

During heat recovery, the temperature was kept at 480 ° C. for about 10 minutes, and the film thickness of 4.3 nm almost matched the film thickness of the amorphous silicon film formed during this. That is, the silicon film is hardly formed before starting the process.

Several methods for obtaining a single crystal layer by epitaxial growth using the solid phase growth technique have been reported.
All of these are methods of removing a natural oxide film by using a reduction reaction at high temperature.

On the other hand, the present invention is a method based on the viewpoint that the oxide film on the surface is not removed but rather reoxidized.

An example of the procedure when the present invention is applied to the solid phase growth process is shown below. A CVD device is used for forming the amorphous silicon film.

Pretreatment (removal of natural oxide film) 0.5% HF solution for 3 minutes, water washing for 5 minutes, rinser drying-Introduction of wafer into CVD apparatus for 15 minutes, vacuum exhaust (0.005 Torr) -Heat recovery for 65 minutes Si ₂ H ₆ / Ar = 100 / 4000SCC
Formation of amorphous silicon film (film thickness about 100 nm) 480 ° C., 30 minutes, Si ₂ H ₆ = 100 SCCM, 0.
The rationale for setting the 3 Torr heat recovery time to 65 minutes is as follows.

FIG. 14 shows the results of measuring the temperature change during heat recovery by introducing a thermocouple thermometer inside the furnace of the CVD apparatus.

As shown in FIG. 14, when the temperature is started by introducing the wafer into the furnace controlled at 300 ° C., the thermocouple temperature becomes constant after 20 minutes of loading time. Furthermore, when the temperature was raised to 480 ° C. which is the film forming temperature of the amorphous silicon film, the temperature in the furnace became almost constant after 45 minutes. From this result, the heat recovery time (time to wait for the start of the process until the substrate temperature reaches a predetermined temperature) was set to 65 minutes.

In this solid phase growth process, as shown in FIG. 15, the substrate surface after removal of the natural oxide film is suppressed to reoxidation to the extent that epitaxial growth is possible due to the effect of inhibiting oxidation of silicon by disilane gas (Si ₂ H ₆ ). It was possible to deposit amorphous silicon.

FIG. 15 shows that in the above method, the temperature (loading temperature) of the furnace when introducing the silicon substrate (silicon wafer) into the CVD furnace and the atmosphere during the heat recovery depend on the interface between the silicon substrate and the amorphous silicon film. It is a figure which shows the result of having investigated what kind of influence it has on the amount of oxidation.

The heat recovery time is 65 minutes. The flow rate and pressure of Ar are 4000 sccm, respectively.
1.2 Torr, N ₂ flow rate and pressure are 1
000 sccm, 0.2 Torr, SiH ₄ / A
The flow rate of r is 150 sccm / 4000 sccm, Si ₂
H ₆ / Ar flow rate is 100 sccm / 4000 sccm
It is.

From FIG. 15, it can be seen that the amount of oxidation depends more on the atmosphere in the heat recovery than on the loading temperature. That is, it is understood that the oxidation can be suppressed by introducing Si ₂ H ₆ into the furnace. Such an oxidation suppressing effect was similarly obtained by using trisilane or tetrasilane instead of Si ₂ H ₆ . Note that an inert gas such as helium or nitrogen may be used instead of the argon gas.

FIG. 16 shows the results of observing the single crystal silicon thus formed and the silicon of the comparative example using a transmission electron microscope. Solid phase growth was performed at 600 ° C. in a nitrogen atmosphere for 2 hours. The atmosphere in FIG. 16A is Si ₂ H ₆ / Ar, and the atmosphere in FIG. 16B is Ar (comparative example).

As shown in FIG. 16 (b), only Ar is used for S
When i ₂ H ₆ was not introduced (Comparative Example), crystal defects were observed because the amount of oxygen at the interface was large. Twins were particularly numerous as crystal defects. The characteristics of the device manufactured using such a substrate were extremely low. On the contrary,
As shown in FIG. 16A, when Si ₂ H ₆ was introduced (the present invention), no crystal defect was observed and the crystallinity was obviously improved.

The inventors of the present invention determined the very initial oxidation amount of less than one atomic layer that occurs in a CVD apparatus.

The amount of oxygen is 1.3 in the surface density of single crystal silicon.
6 × 10 ¹⁵ atoms / cm ² (Si density: 5.0 × 10 ²² atoms / cm ³ ) was shown as 100%.

After holding at 480 ° C. in Ar for 1 to 69 hours, an amorphous silicon film was deposited on the silicon substrate, and the amount of oxygen trapped at these interfaces is shown in FIG.

As shown in FIG. 17, in 10 hours or less,
The interfacial oxygen content increases as the holding time increases. However, even if held for a longer time, the amount of oxidation does not increase. The H ₂ O partial pressure in the apparatus atmosphere was 7 × 10 ⁻³ Torr (13
3 Pa), which does not change in 2 hours as shown in FIG.

However, as shown in FIG. 17, when Ar was continuously introduced for 60 hours or longer, the amount of oxidation was no longer proportional to the holding time. In this case, the H ₂ O partial pressure is considered to have decreased.

The white circles shown in FIG. 17 are the amounts of oxidation on the surfaces of the two amorphous silicon films obtained by repeatedly forming the amorphous silicon films. The black circles represent the oxidation amount of the silicon substrate when held for 2 hours in an Ar atmosphere, which was obtained from the difference between the oxygen amount at the interface between the two amorphous silicon films and the oxidation amount at the interface between the silicon substrate and the amorphous silicon film. is there.

The obtained oxidation amount of 30% / 2 hours is as shown in FIG.
As shown in, the amount of oxidation on the surface of the amorphous silicon film was almost the same. Regarding oxidation in the device, no difference was observed between the silicon substrate and the amorphous silicon film.

When Ar was continuously introduced into the apparatus for about 60 hours, the amount of oxidation became not proportional to the time of holding in Ar atmosphere. FIG. 18 shows the results of measuring the amount of oxidation when the device history was changed and the device was held for 1 hour in an Ar atmosphere.

In FIG. 18A, after continuously introducing Ar into the apparatus for 69 hours, an amorphous silicon film was formed, and the surface thereof was exposed to Ar atmosphere for 1 hour, and the interfacial oxygen amount at that time was obtained. The result.

As shown in FIG. 18A, Ar for 69 hours
The amount of oxidation was 1% during 1 hour, which was 40% before introducing
% Or less. However, when the apparatus was once opened, the wafer was newly reloaded and the oxygen was determined when the wafer was kept in the Ar atmosphere for 1 hour, the oxygen content was again 40%.

FIG. 18 (b) shows that Ar was introduced for 66 hours and 1
This is the result of examining the change in the amount of oxidation by stopping the introduction of Ar and introducing N ₂ or air instead of Ar after the oxygen amount in the time became 1% or less.

As shown in FIG. 18B, N _{2 is set} to 0.1
When introduced for 3 hours at Torr, no increase in oxygen content was observed. The effect of stopping the supply of Ar once was not observed. On the other hand, when air was introduced for 1 hour, the oxygen amount returned to the initial state before Ar was introduced for a long time.

Here, in particular, H ₂ O formed by the wafer is used.
In order to reduce the amount of adsorption,
Only the six wafers needed to measure the interfacial oxygen content were used.

The air in the clean room is maintained at 24 ± 1 ° C. and humidity of 48 ± 2% throughout the year as shown in FIG. Since the saturated vapor pressure at 24 ° C. is 22.5 Torr, the H ₂ O partial pressure is as high as 11 Torr.

Therefore, it is considered that the reoxidation of silicon in the apparatus was caused by H ₂ O supplied from air and adsorbed to the pipes other than the wafer.

FIG. 20 shows the results of obtaining the temperature dependence of the oxidation rate by changing the temperature in the sequential depot experiment.

At a low temperature of 400 ° C. or lower, the undoped amorphous silicon film is formed at a low rate, so a boron-doped amorphous silicon film was used. As shown in FIG. 20, the oxidation rate is 1/300 at 300 ° C. compared to 480 ° C.
Reduced to 5.

At 400 ° C. or lower, since the boron-doped amorphous silicon film is oxidized, activation energy and the like are not required here, but the oxidation rate does not decrease rapidly as the order changes.

As shown in FIG. 20, at room temperature / in air,
The oxidation rate is 2% / h, which is an extension of the dotted line in the figure.

After treatment with 0.5% HF for 3 minutes, washing with water for 5 minutes and drying with a rinser, the product was immediately introduced into the apparatus to form an amorphous silicon film. When the amount of dissolved oxygen in pure water is 300 ppb, the amount of reoxidation on the surface of the substrate does not depend on the time of washing with water, but largely depends on the time of standing until it is introduced into the apparatus.

FIG. 21 shows the interfacial oxidation amount in the case where the pretreatment with sufficient hydrogen termination was manually performed and in the case where the automatic pretreatment apparatus was used. The amount of interfacial oxygen after depositing the amorphous silicon film was determined by SIMS analysis.

In order to carry out the treatment more effectively using the automatic pretreatment apparatus, after the treatment for 3 minutes with 0.25% HF, the deionized water is overflowed so that oxygen does not enter and HF is replaced.

As shown in FIG. 21, there is no difference between the manual work and the automatic pretreatment device. However, after the pretreatment, when stored in an auto carrier and left in a clean room for one day, the amount of oxidation increased as compared with the case where the pretreatment was stored in an N ₂ purge box. The N ₂ purge box is made of aluminum. Further, the atmosphere was replaced with N ₂ gas passed through a purifier.

As shown in FIG. 21, after the pretreatment, the oxygen amount increases as the time left in the atmosphere becomes longer. Therefore, when stored in the N ₂ purge box, reoxidation can be suppressed.

When a wafer treated with dilute hydrofluoric acid is introduced into a CVD apparatus and the atmosphere for heat recovery is set to Si ₂ H ₆ , even if the ultimate vacuum is 1 × 10 ⁻³ Torr, the amorphous silicon film and the silicon substrate are The amount of oxygen at the interface with and was suppressed to 20% or less of the silicon atom density, and stable solid-phase epitaxial growth was possible.

The present invention is not limited to the above embodiment. For example, although the number of semiconductor devices is one in the above description, the present invention provides two semiconductor manufacturing devices.
It is also applicable when connecting more than one unit.

That is, when two or more semiconductor manufacturing apparatuses are connected, even if the ultimate vacuum of the connecting sections is not sufficiently high, the reducing gas is flown through the connecting sections to connect the two or more semiconductor manufacturing apparatuses. Oxidation can be effectively prevented while the substrate (wafer) moves back and forth.

Further, when the substrate (wafer) is taken in and out at the connection portion, it is not necessary to evacuate to a high vacuum, and the time taken for taking in and out can be shortened. Specifically, it takes 10 hours or more to exhaust to a pressure of 1 × 10 ⁻⁸ Pa, which is a pressure that can hold a wafer without oxidation for 1 hour or more, by the exhaust method using a normal turbo pump or the like. Then, it is possible to suppress the generation of oxidation by flowing the reducing gas for only 5 minutes of exhaust.

Besides, various modifications can be made without departing from the scope of the present invention.

[0134]

As described in detail above, according to the present invention, by introducing the gas containing the reducing gas before introducing the film forming gas into the container, the oxidizing substance remaining in the container can be eliminated. It becomes possible to prevent the oxidation and the oxidation due to the introduction of the oxidizing substance remaining outside the container into the container at low cost.

[Brief description of drawings]

FIG. 1 is a process sectional view showing a method for forming a MOS transistor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a schematic configuration of a CVD apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing an experimental system.

FIG. 4 is a diagram showing a relationship between vacuum evacuation time and residual gas partial pressure.

FIG. 5 is a diagram showing the relationship between Ar introduction time and residual gas partial pressure.

FIG. 6 is a diagram showing changes in residual gas partial pressure when the valve is opened and closed.

FIG. 7 is a diagram showing a change in residual gas partial pressure when the temperature of the CVD furnace is raised.

FIG. 8 is a diagram showing changes with time in the partial pressure of residual H ₂ O in the CVD furnace.

FIG. 9 is a diagram showing the atmosphere dependency of the amount of oxidation.

FIG. 10 is a diagram showing a typical example of the results of a sequential depot experiment.

FIG. 11 is a diagram showing pressure dependence of interfacial oxidation amount.

FIG. 12 is a diagram showing the equilibrium oxygen partial pressure.

FIG. 13 is a diagram showing the result of reduction measurement with Si ₂ H ₆ .

FIG. 14 is a diagram showing a temperature change during heat recovery.

FIG. 15 is a graph showing the relationship between loading time, atmosphere, and interfacial oxidation amount.

FIG. 16 is a micrograph showing a crystal structure.

FIG. 17 is a diagram showing the relationship between the time of holding in an Ar atmosphere and the interfacial oxidation amount.

FIG. 18: Change device history to 1 in Ar atmosphere
The figure which shows the measurement result of the amount of oxidation when hold | maintaining for a time

FIG. 19 is a diagram showing temperature and humidity in a clean room.

FIG. 20 is a graph showing temperature dependence of oxidation rate.

FIG. 21 is a diagram showing the relationship between pretreatment, storage method, and interfacial oxidation amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Element isolation insulating film 3 ... Amorphous silicon film 3a ... Single crystal silicon film 4 ... Gate oxide film 5 ... Gate electrode 6 ... Gate side wall insulating film 7 ... Source region 8 ... Drain region 9 ... Source electrode 10 ... Drain electrode 21 ... CVD furnace (film forming chamber) 22 ... Substrate (wafer) 23 ... Heater 24 ... Process gas introduction pipe 25 ... Mass flow controller 26 ... Filter 27 ... Valve 28 ... Inert gas introduction pipe 29 ... Mass flow controller 30 ... Filter 31 ... Valve 32 ... Reducing gas introduction pipe 33 ... Mass flow controller 34 ... Filter 35 ... Valve 36 ... Dry pump

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Yamazaki 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (2)

[Claims] 1. A step of housing a semiconductor substrate in a container, a step of introducing a gas containing a reducing gas into the container until the inside of the container reaches a film formation temperature, and the reducing gas in the container. And a film forming gas is introduced into the container to form a film on the semiconductor substrate. 2. A semiconductor device, wherein the semiconductor substrate is a silicon substrate, and the film forming gas is one gas selected from disilane gas, trisilane gas and tetracine gas, or a mixed gas of two or more gases. Production method.